Electrode with multiple carbon fibre contact surface

ABSTRACT

An electrode having a contact surface with the electrolyte consisting of a number of carbon fibers (1), and a method for the manufacture of an electrode where a number of carbon fibers (1) are wound into a carbon fiber skein (2) whereupon the skein (2) is gathered together at a connection area and embedded to form a connecting stud (5), which is then treated so that the end surfaces (6) appear of all the carbon fibers gathered together in the connecting stud (5), after which the carbon fiber end surfaces (6) are connected to a signal conductor (8). And an antenna (12) comprising electrically connected electrodes where the contact surface of each electrode with the electrolyte consists of a number of carbon fibers (1).

TECHNICAL FIELD

The present invention relates to the technique of achieving a large areaof contact and a good connection between a conductive electrode and theelectrolyte which is in contact with the electrode. The electrolytecould for instance be in the form of either salt water or fresh water.Such an electrode with water as electrolyte can be used for measuringpurposes or as a part of an antenna construction. With this large areaof contact, very small changes in electrical fields can be measured,whereby the electrode can be used for instance for measuring ofwater-currents.

BACKGROUND OF THE INVENTION

For detecting changes in the electrical field under water, pairs ofdifferent kinds of electrodes, made of zinc, graphite, silver/silverchloride etc., have previously been used. They have all had theirbenefits and drawbacks, such as silver/silver chloride electrodes havinghigh sensitivity but at high costs, zinc electrodes having a low pricebut being mechanically or electrically instable, and graphite electrodeswhich are difficult to manufacture according to defined specificationswithout discarding. Large active areas have required large physicaldimensions and have, in connection with graphite electrodes, causedirreproducible properties conditioned by small chemical or morphologicalvariations. Consequently, there are significant problems with thepreviously available techniques.

PURPOSE OF THE INVENTION

The purpose of the invention is to solve these problems by providing anelectrode based on bundles of carbon fibres which are connected to adesired conductor, and a method for manufacturing this electrode. Afurther purpose of the invention is to provide an underwater electrodehaving much better performance characteristics than previously availableunderwater electrodes. Furthermore, the purpose of the invention is toprovide an antenna mainly for underwater measurements.

SUMMARY OF THE INVENTION

An electrode according to the invention is provided with tufts orbundles of carbon fibres which have been cleaned along the fibresurfaces to get a good electrical contact with surrounding water, andwhich, furthermore, have been gathered together at one end and connectedto an electrical conductor.

Such a manufactured electrode constitutes, together with an electrode ofthe same kind, a pair of electrodes which has turned out to have goodantenna properties in water. Furthermore, it is comparatively easy tomanufacture. As the electrode is made by carbon fibres, which have ahomogenous chemical structure all along the fibres, an electrode havingreproducible properties is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a step in the manufacture of a device according to the isinvention.

FIG. 2 shows a further step in the manufacture of a device according tothe invention.

FIG. 3 shows a cross-sectional view according to FIG. 1.

FIG. 4 shows a first embodiment of the invention.

FIG. 5 shows a second embodiment of the invention.

FIG. 6 shows an antenna according to the invention.

DESCRIPTION OF THE INVENTION

An electrode according to the invention is produced by winding a bundleof carbon fibres into a carbon fibre skein 2, which is then gatheredtogether at a connection area where the carbon fibres are bound togetherto form a connecting stud 5, which is then treated so that the endsurfaces 6 will appear of all the carbon fibres gathered together in theconnecting stud 5, after which the carbon fibres are connected to asignal conductor 8 through their end surfaces 6.

The electrode according to the invention is suitably produced, see FIG.1, by winding carbon fibres 1, in the form of a bundle of generally 6000carbon fibres, approximately 50 turns around two end poles 3,4 with anintermediate distance of about half a meter, into a skein 2. Thesechosen values of the number of carbon fibres, the number of turns andthe distance, will result in an electrode having approximately 600 000carbon fibre ends for connection to a signal conducting cable. Withthese values, the area of contact with the electrolyte will be fully 3m².

The oblong skein 2 of fibres is loosened carefully and is fixed in themiddle thereof, for instance with a piece of shrinkage hose. Aftercutting in the middle of the piece of shrinkage hose, the ends of thetwo carbon fibre bundles fitted with hose are embedded in epoxy plasticin vacuum so that a connecting stud 5 is formed, see FIG. 2, which aftercuring is shaped by means of grinding tools. The connecting stud 5 isgrinded until all the end surfaces 6 of the carbon fibres appear in thegrinding surface, see FIG. 3. On these carbon fibre end surfaces ametallic coating is applied, see FIG. 4, which forms a connecting plate7 for connection of a signal conducting cable 8. After the connection,the connection place is embedded in epoxy plastic to form a protectivecover 9 for shielding the contact surfaces from water influence.Thereafter, the epoxy coating which the fibres have been given duringtheir manufacture is cleaned off from the fibre surfaces. This coatinghas generally been applied to improve the wetting properties of thefibres and their ability of binding to an epoxy matrix, and itconstitutes a layer having insulating properties. Through the cleaning,the fibres, and thereby also the electrode, have been adapted for use inelectro-chemical applications. The cleaning is carried out in a normalway with different solvents, for instance with acetone, alcohol andwater in turns. Between the different steps in the manufacturing processit is checked that none of the individuals differ in various aspectsfrom empirically obtained set values, to make sure that the differentindividuals in a manufacturing process are as equal as possibleregarding for instance electric resistance, length etc.

The manufacturing process is finished by cutting open the loop-shapedcarbon fibre tufts 10, if a brush-like appearance with a lot of fibreends sticking out in the water is desired, see FIG. 4. Otherwise thecarbon fibres remain in a loop-shape, see FIG. 5, so that an attachmentis possible in both ends, whereby a similar utilization in water ispossible independent of the spatial orientation of the attachment. Finalassembling with mounting ears 11 for mechanical fixation and with awater permeable flow protection around the fibres is done in the easiestway, after which final testing and verification of the individuals, i.e.each electrode, is done in laboratory.

Another possible method of manufacturing is to form the connecting stud5 at first, by making an embedment at the middle part of the carbonfibre skein 2, after which the connecting stud 5 is bisected and thecarbon fibre end surfaces 6 of each bisecting surface are connected to asignal conductor 8 in the way mentioned above. The connection place isthen embedded and the fibres are cleaned in accordance with what ismentioned above.

With the present type of electrode a large active area of an inert kindwith small external physical dimensions and an extremely highreproducibility and mechanical durability is combined in a new way witha simplified manufacturing technique. Two electrodes can also becombined to form a reliable and cost effective antenna 12, see FIG. 6,for detecting variations in the electrical field under water.

Possible utilizations include could be scientific measurements of thegeological E-field, measurement of sea-heave and water-currents,detection and measurement of ship movements, or signal transmissionbetween water vessels or divers with limited range of voice messages.

What is claimed is:
 1. An electrode having a contact surface that isable to contact an electrolyte, wherein the contact surface includes aplurality of carbon fibres, with at least one of their two ends gatheredtogether and electrically connected to a signal conductor through endsurfaces of the carbon fibres.
 2. The electrode according to claim 1,wherein the carbon fibres in both of their ends are gathered togetherand electrically connected to the signal conductor.
 3. A method for themanufacture of an electrode, wherein a bundle of carbon fibres is woundinto a carbon fibre skein, after which the carbon fibre skein isgathered together at a connection area where it is bound together toform a connecting stud, that the connecting stud is treated to make theend surfaces appear of all the carbon fibres gathered together in theconnecting stud, and that the carbon fibre end surfaces thereafter areconnected to a signal conductor.
 4. The method according to claim 3,wherein the connecting stud is formed by making an embedment of thecarbon fibre skein at the connection area, and that the connecting studthereafter is bisected whereupon the carbon fibre end surfaces of eachbisecting surface are connected to the signal conductor.
 5. The methodaccording to claim 3, wherein the carbon fibre skein is cut in theconnection area whereupon thereby obtained end piece is embedded, andthat the connecting stud formed by the embedment is grinded until allthe end surfaces of the carbon fibres appear in the grinding surface. 6.The method according to claim 3, wherein the signal conductor isconnected to the carbon fibre end surfaces through a metallic coatingwhich is applied on the carbon fibre end surfaces.
 7. The methodaccording to claim 6, wherein the connecting stud, the carbon fibre endsurfaces, the metallic coating and a part of the signal conductor areembedded in a polymeric substance to form a protective cover.
 8. Themethod according to claim 7, wherein the carbon fibres used for themanufacturing of the electrode have an epoxy coating which is cleanedoff from the fibre surfaces by means of different solvents.
 9. Anantenna comprising electrically connected electrodes, each electrodehaving a contact surface that is able to contact an electrolyte, whereinthe contact surface of each electrode with the electrolyte includes aplurality of carbon fibres with at least one of their two ends gatheredtogether and electrically connected to a signal conductor through endsurfaces of the carbon fibres.
 10. The antenna according to claim 9,wherein the carbon fibres in both of their ends are gathered togetherand electrically connected to the signal conductor.